Such a method, such a control unit and such a use are described in German Patent Application No. DE 199 00 740. This document refers to a known torque monitoring for an Otto engine, in which an actual torque of the internal combustion engine is determined from the rotary speed, combustion chamber charge (air mass) and the ignition angle setting. In addition, this document broadens the known torque monitoring to cover internal combustion engines that, at least from time to time, are operated using a lean fuel/air mixture. Examples of such internal combustion engines are Diesel engines and Otto engines having direct injection in an operation having stratified combustion chamber charging. Such internal combustion engines mostly operate unthrottled, so that their combustion chambers are usually charged with a maximum air mass. The torque is then set via the injected fuel mass (quality control), whereas in Otto engines that are operated throttled the torque is set via the mass of the combustion chamber charge with fuel/air mixture (quantity control).
It is proposed in this document, for torque monitoring in connection with a quality controlled internal combustion engine, to determine the actual torque based on the injected fuel mass as the torque-determining variable. In this context, the admissible torque is determined via the driver's command and/or the rotary speed from a characteristics map or by a simplified function model. In this context, the formation of the torque-determining signals for controlling a power actuator takes place in a control unit on a first program level, during the formation of the admissible torque within the scope of a monitoring concept on a second program level.
However, ascertaining the torque from the driver's command, especially in internal combustion engines having fault regulators in transient operation states, especially upon transition into overrun condition, is not reliable, since (admissible) interventions of the fault regulator influence the formation of the control signal for a power actuator. The actual torque that results from the control signal, therefore, has the fault intervention superposed on it. This may lead to detection errors in the usually formed value for the admissible torque.
An internal combustion engine control having a fault regulator is described in German Patent No. DE 195 37 787. The known fault regulator has a D2T2 (dye diffusion thermal transfer) component having operating point-dependent differential time constants and delay constants as parameters. The D2T2 component filters the rotary speed of the internal combustion engine. Its output signal is linked additively with the driver's command-dependently produced control signal for the power actuator. Vibrations of the powertrain, that are perceptible as jerking, are superimposed on the rotary speed as interference. The jerking vibration of the powertrain is damped by the coupling in of the filtered rotary speed signal into the control signal for the power actuator.
Because of the coupling in of the filtered rotary speed signal into the activating signal formation, the jerking vibration images in the control signal for the power actuator, and therewith finally also in the temporal course of the torque actually produced by the internal combustion engine. Jerking vibrations are induced especially by torque changes, as appear, for instance, during transition into overrun condition.
In the following, by overrun condition of an internal combustion engine there is understood an operation in which the internal combustion engine outputs no torque, but rather is driven itself by external influences. Overrun condition appears, for instance, during braking or downhill travel of a motor vehicle, if the driver does not request any torque. The transition into overrun condition may be recorded, for example, by a driver's command sender, for example an accelerator sensor.
The fault regulator intervenes in the control signal formation, particularly during transition into overrun condition, so that the known rotary speed monitoring, that is based on an evaluation of the driver's command is not reliable until the fault regulator intervention has decayed. In this connection it is known per se that one should wait about one second, in response to transition into overrun condition, so as to let the fault regulator intervention decay. The torque monitoring is released only after that. This torque monitoring is therefore not continuous. With that, the disadvantage is connected that a faulty torque generation is discovered only after a delay corresponding to the waiting period. However, for safety reasons it is desirable to detect an undesired generation of torque with the least possible delay, in order to be able to trigger an error response.